The following is a summary of the results of our work at this moment have not yet been published: (1) The results that the C14-GCA test is a useful tool to evaluate the adequacy of small bowel bypass procedures for morbid obesity and also in following the adaptive response after surgery. (2) Hepatic bile lithogenicity fluctuates from day-to-day and single determinations are not too significant in determining the true lithogenic potential of bile. A deficiency of cholesterol-7- -hydroxylase probably does not play a role in human bile lithogenesis. (3) There is an increased incidence of biliary and urinary calculi following bowel bypass procedures: The etiology of the urinary calculi is based on persistent hyperoxaluria, whereas an increase in the biliary glycine/taurine ratio is probably the etiologic agent for the biliary calculi. (4) The liver has the ability to significantly increase the synthetic rate of the two primary bile salts (GC and GCDC) to compensate for excess fecal loss: in spite of this however, there is a contraction of the bile salt pool after bypass procedures. (5) The excessive fecal loss of bile salts plays a greater role than the fecal free fatty acid loss in the pathogenesis of diarrhea after small bowel bypass. (6) A deficient collagen and vascular response probably plays a role in the mechanism of suture line dehiscence after colonic anastomosis.